1. Field of the Invention
The present invention relates to an electrochemically luminescent display device which induces a chemical reaction as a voltage is applied thereto, thereby enabling the display device to chemically emit light.
2. Description of the Related Art
Although there are persistent expectations for the application of an organic electroluminescent (EL) display device to a display device due to the capabilities thereof for full-color display and for reducing the thickness of the device, there are various drawbacks accompanied with the injection of electric charges. As means for overcoming these drawbacks, there has been developed an electrochemically luminescent (ECL) display device utilizing electrochemical luminescence, wherein a chemical reaction is induced by the application of voltages to the display device, thereby enabling the display device to chemically emit light.
Since the light-emitting layer of the ECL display device is constituted by a liquid exhibiting fluidity, the materials of the light-emitting layer are more liable to circulate as compared with an organic EL display device wherein the light-emitting layer thereof is constituted by solid materials. Therefore, the ECL display device can be hardly suffered from defective fixed points such as defective sticking and hence the ECL display device is generally excellent in reliability. Further, since the ECL display device is constituted by a mono-layer structure comprising a solution of electrochemically luminescent materials, and electrodes for applying an electrical potential to the solution, it is not required to laminate a charge-transporting layer which is required in the case of the organic EL display device. Because of this, the ECL display device can be manufactured at a lower cost as compared with the organic EL display device. Furthermore, the ECL display device can be actuated at a lower voltage according to the principle based on an electrochemical reaction.
In the case of the ordinary display devices, the optical characteristics thereof can be controlled through the application of a potential difference by a couple of electrodes. On the other hand, in the case of the ECL display device, since an electrochemical reaction is utilized for the emission of light, it is required to control the optical characteristics thereof by accurately applying the oxidation-reduction potential of a light-emitting material since an electrochemical reaction is utilized for the emission of the ECL display device. In the case of a 2-electrode system, it is not clear how the potential difference that has been applied to the display device is distributed to a couple of electrodes, so that it is impossible to make clear as to at what level the electrical potential of each of these electrodes is existed. Because of this, it is required to express the electrical potential of these electrodes by an electrode (reference electrode) that can indicate a prescribed electrode reaction to be used as a certain standard.
In JP-A 10-135540 (KOKAI), there is proposed an electrochemically luminescent cell, which comprises a solution of electrochemically luminescent materials, an electrode for applying an electrical potential to the solution, a reference electrode acting as a standard, and a vessel for housing the solution and these electrodes. This patent document however fails to specifically describe the size and structure of the reference electrode. Since the reference electrode is an electrode functioning as a standard for electrical potential, if this reference electrode has deteriorated, it would become impossible to control so as to secure a stable electrical potential, thus making it difficult to obtain a display device exhibiting sufficient emission efficiency and excellent reliability.